*Optional: you can add the onions to this mixture or layer them in the casserole. It doesn’t make too much of a difference. I personally like to add them at this stage and let them get coated in the sauce. Pour the almond milk into a large bowl. Whisk in nutritional yeast and other spices, stirring well. Slowly add the kale to the mixture, making sure it gets well coated. In a glass baking dish, pour a thin layer of kale au gratin sauce into the bottom of the dish. Add a thin layer of sweet potato, slightly overlapping them, followed by another layer of kale. Make sure you some have the kale au gratin sauce left over at the end to pour over the casserole when finished.